To this point, Frank Marshall spent about a decade working on what we now call the Marshall Attack, specifically to play it against Capablanca. Capablanca refuted it over the board without ever having looked at it.
The problem with the question "when should I study openings" is that it is almost always asked by players well below the 2000-rating mark (usually by players 1200 and lower). They think their opponents are booked up. In reality, most 1200s have no clue what they are doing in the opening, but that isn't what is causing them to lose games. In fact, nearly 100% of the time, the reason those players lose games is due to tactical weaknesses.
That is not to say that those players shouldn't spend any time working on their openings, but that they should do it a specific way. Namely, as part of studying whole games. The method I recommend is to find players you enjoy watching and play through their games. You will pick up their opening ideas (and you can be pretty sure that if they are in the top 100, they are not blundering material in the opening) while learning the middlegame plans and endgame technique. Additionally, when you play a game and analyze it, look up where the game left known book lines and/or where you deviated from the lines you had studied (no one can remember everything!) Make mental notes "okay, so he played here and I was supposed to play X, but I messed up and played Y ... why does X work and Y not work?" When you understand why a move cannot be played, you won't make the same mistake again.
There was a recent Perpetual Chess episode where GM Eugene Perylshteyn (sp) was explaining that he has met quite a few GMs who had very little knowledge of opening theory. So it is quite apparent that there is no need to study opening theory (i.e. memorizing moves) at the club level. Besides, suppose you spent the next 6 months memorizing all the lines in the Sicilian, and then you run into someone who plays like this:
Now all that time was spent doing something that doesn't help you at all because the opponent has you "out of book" on move 1 (granted, that approach can win you some games - as it did here when I lost on time in a winning position, but you are not getting better at chess by doing so).
As for Capablanca, unsurprisingly he didn't recommend ignoring the opening
"... The game might be divided into three parts, i.e.:- 1. The opening. 2. The middle-game. 3. The end-game. There is one thing you must strive for, to be equally efficient in the three parts. Whether you are a strong or a weak player, you should try to be of equal strength in the three parts. ..." - from Capablanca's book, My Chess Career